In order to joint drill string components for percussive rock drilling it is well known to use so called trapezoidal threads, wherein one end of a drill string component comprising a male thread is threaded together with a female thread at an end of the next drill string component. Alternatively, both ends of drill rods to be joined are threaded together over sleeves being provided with female threads at both ends.
Thread joints for drill string components or percussive rock drilling are subjected to high instantaneous loads and hostile environments. The threaded joints have to be drawn to moment levels that prevent loosening during operation, which means that large forces influence the respective thread wall of the male as well as the female thread. The working life length of the drill string components is related to the ability of the thread joints to resists the loads they are subjected to during operation. For that reason it is desired to provide threaded joints having the ability to better resists these loads and thereby give the components prolonged working life.
Another important aspect is producibility at low cost.
From U.S. Pat. No. 4,040,756 is previously known a threaded joint with inclined thread tops. When it concerns thread bottoms of the female as well as of the male thread, they are, however, provided with continuously curved configuration. The thread bottoms are going evenly, tangentially, over into adjacent thread flanks.
As further examples of the background art can be mentioned U.S. Pat. Nos. 6,196,598 and 4,687,368, whereof the latter concerns a more traditional trapezoidal thread.